The present invention relates to a method for contactless treatment of a substrate such as a semiconductor wafer, comprising enclosing the wafer in an apparatus and applying two gas streams, in opposing directions, from first and second side sections located opposite on another, to the two opposing planar sides or surfaces of the wafers.
A method of this general type is disclosed in Netherlands Laid Open Application 8402410, in which furthermore, reference is made to Netherlands laid Open Applications 8103979, 8200753 and 8203318.
From these publications it is known to position a wafer such that it is floating between the two side sections. If the gas flow is suitably chosen, it has been found that a highly accurate definition of the position of the wafer with respect to the side sections is possible and this position is relatively fixed, that is to say little variation occurs in the position of the wafer with respect to the side sections. In the patent publications concerned it is described that the wafer is subjected to a wet treatment and is then possibly dried. For the purposes of drying, the gas which holds the wafer in place is heated to about 100.degree. C. and is moved over the surface of the wafer, as a result of which the moisture present is automatically removed.
Heating to much higher temperatures in the range of 200.degree.-1200.degree. C. is frequently necessary when treating semiconductor substrates. Heating can involve annealing or raising the temperature to make deposition or other processes possible. In the prior art, wafers are to this end placed in furnaces and then heated. Although this method is adequate, it has at least two disadvantages. Firstly, a method of this type is usually not completely contactless, that is to say certain points of the wafer are supported. Secondly, it takes a relatively long time to heat a wafer. This is due not so much to the thermal capacity of the wafer itself as to the relatively slow heat transfer between the furnace and the wafers and to the fact that in order to achieve a controlled, deformation free heating of the wafers, the wafers need to be heated inside the furnace together with the furnace itself.
In order to solve this problem single wafer systems have been disclosed with which rapid heating was achieved with the aid of high power lamps (50-80 Kw). Such a method is particularly expensive and difficult to control.
U.S. Pat. No. 4,622,918 discloses an apparatus wherein a wafer is fed through between a number of columns located some distance apart. Sets of columns located opposite one another, between which the wafer moves, are likewise some distance apart. In the gap between the sets of columns, heating is effected by means of a lamp some distance away. This apparatus has the drawback that due to the presence of many metal parts with complicated constructions in close proximity to the wafer, only heating to limited temperatures is possible. Furthermore, in this apparatus a wafer is supported by a plurality of columns of air streams with gaps in between the columns. Due to the succession of columns, where the wafer is supported, and gaps between the columns where the wafer is exposed to the heat radiation of the lamps, both the support of the wafer and the heating are not homogeneous.
It has been found that only limited heating can take place effectively by heating the gases, as is described in the above-mentioned Netherlands applications.